Wednesday, September 19, 2007

MIVEC System

In the early ‘90s, Mitsubishi Japan introduced a valve control system to combat Honda’s VTEC design. This system is labelled MIVEC (Mitsubishi Innovative Valve and Lift Electronic Control System).

In its simplest form, MIVEC switches between two different intake and exhaust cam lobes depending on engine rpm. At low rpm, the valves receive relatively modest lift and opening duration. At high rpm, the secondary cam lobe is engaged and the valves receive greater lift and duration (which results in increased overlap).

The purpose of the secondary cam lobe is to deliver greater engine breathing and the ability to maintain torque at very high rpm (which means greater power). The MIVEC system achieves its high power without the driveabililty, fuel consumption and emissions trade-offs typical in a conventional engine.

In addition to the base MIVEC principle, Mitsubishi also released a sophisticated MIVEC-MD (Modular Displacement) system in the ‘90s.

The MD system is an early form of cylinder deactivation which involves closing the intake and exhaust valves at light engine load. This means the driver must open the throttle further to maintain power and, as a result, pumping losses are reduced and active cylinder pressures are increased. This results in greater efficiency and fuel economy.

Depending on conditions, the MIVEC-MD system can reduce fuel consumption by 10 – 20 percent.

The 1990s...

The first production car to appear with MIVEC technology was the Japanese-market Mitsubishi Mirage Cyborg of late 1992. The Cyborg packs a magnificent little 1.6-litre transverse four boasting DOHC, 16 valves and, of course, variable valve lift and duration. With a high 11:1 compression ratio (making premium unleaded fuel mandatory), the 4G92 MIVEC 1.6 screams out 129kW at 7500 rpm and 167Nm at 7000 rpm. To put things into context, that’s about 10kW more than the famed Toyota 4A-GE 20 valve and Honda VTEC 1.6 engines!

A MIVEC MD (Modulated Displacement) version was also available. The MD engine makes the same power but with superior fuel economy. Unfortunately, it appears that the MD version was dropped in 1996.

With a close-ratio 5-speed manual or 4-speed auto driving the front wheels, the Mirage Cyborg is one of the most responsive and fastest hatchbacks ever built – it’s guaranteed to get you pumped up! The MIVEC Mirage was continued until 1999.

Also sold in Japan from 1992 was the MIVEC-powered Lancer MR sedan. The Lancer MR uses the same mechanical configuration as the Mirage Cyborg (which means 129kW and 167Nm). A Modulated Displacement version was available to order but was axed in 1996.

The final application of the 4G92 MIVEC engine was in the 1994 Mirage Asti RX coupe. There were no mechanical changes to the engine. The Asti MIVEC range was later expanded to include R and ZR models. The Modulated Displacement engine was not offered. The MIVEC Mirage Asti lasted until 1999.

The second MIVEC engine joined the stable in late 1993.

The MIVEC 2-litre V6 (coded 6A12) debuted in a Japanese-market medium size sedan known as the Mitsubishi Eterna Visage R. The small capacity V6 isn’t as highly tuned as the MIVEC 4G92 four but in manual form it easily cranks out 147kW - about the same as a contemporary 2-litre turbo engine. Peak power arrives at 7500 rpm while peak torque (200Nm) is found at 6000 rpm. In comparison to the 4G92 MIVEC, this engine runs a relatively modest 10:1 compression ratio, but it still requires premium unleaded fuel.

The Eterna Visage R comes with either a 5-speed manual or 4-speed auto. Interestingly, the auto version is detuned to 143kW but generates 2Nm more torque (202Nm) at the same revs. The Visage R was also available in Modulated Displacement guise from late 1994. The line was discontinued in 1995.

The same 6A12 MIVEC V6 was also fitted in the slightly larger 1993 Galant VX-R and 1994 Emeraude Super Touring R. Again, the 5-speed manual version makes 147kW/200Nm while the auto makes 143kW/202Nm. From late 1994, a MD version replaced the normal MIVEC model - this gave these family-oriented sedans a welcome fuel consumption reduction. The Galant and Emeraude Super Touring R were axed in 1995.

The next application for the 6A12 MIVEC V6 was in the snout of the go-fast FTO coupe.

The FTO was released in 1994 as the spiritual successor to the Galant FTO of the early ‘70s. In top-line GPX trim, the FTO is powered by the 6A12 2-litre V6 with DOHC, 24 valves and MIVEC. Compression ratio remains at 10:1 and, regardless of transmission, it generates 147kW at 7500 rpm and 200Nm at 6000 rpm. The engine comes tied to a 5-speed manual or INVECSII 4-speed auto with sequential shift.

The most powerful MIVEC engine arrived in early 1995 with the Japanese-market Diamante 30M.

The Diamante 30M (recognised as the KE Verada in Australia) is equipped with a 3-litre V6 packing DOHC MIVEC heads. With the same 10:1 compression ratio as the little 2-litre V6, the big 3-litre MIVEC (coded 6G72) roars out 199kW at 7000 rpm and 301Nm at a relatively low 4500 rpm. Premium unleaded fuel is required.

This monster comes tied to a 5-speed INVECSII sequential auto and drives the front wheels. Unfortunately, the MIVEC 6G72 had a very short lifespan – it lasted only until mid 1997 when the GDi engines took over.

The Current Decade...

In early 2004, the Mitsubishi Grandis people-mover became the first vehicle sold in Australia with MIVEC. But be careful how you interpret the application of the MIVEC name...

The MIVEC system in the Grandis is completely unlike the previous high-performance systems that alter inlet and exhaust valve lift and duration. In this incarnation, MIVEC means only variable inlet valve lift and duration.

With a basic SOHC, 16 valve head and a tame version of MIVEC, the Grandis engine (coded 4G69) makes a conservative 121kW at 6000 rpm and 217Nm at 4000 rpm. The MIVEC system switches to its second stage at 3600 rpm. A 9.5:1 compression ratio means no problem using normal unleaded fuel and, indicative of the engine’s modest performance, it’s sold only with a 4-speed automatic with sequential shift.

In late 2004, the Grandis was joined by the updated Outlander which uses the same 4G69 engine. In Outlander guise, the engine makes 120kW at 5750 rpm and 220Nm at 4000 rpm. Ninety-five percent of peak torque is on tap at 2500 rpm. The AWD Outlander is also available with only an auto transmission.

Late 2004 also saw the debut of the all-new Colt.

The Colt is powered by a 1.5-litre four with a DOHC, 16 valve head and MIVEC. The engine (jointly designed with DaimlerChrysler and coded A9) also incorporates electronic throttle control, tubular extractors and low-friction pistons. It appears that, like the 2.4 litre MIVEC in the Grandis and Outlander, this engine has a MIVEC system that operates only the intake valves. With its 10:1 compression ratio, the engine survives with normal unleaded fuel and generates 72kW and 132Nm (at 6000 and 4250 rpm respectively). See Mitsubishi Colt LS Test for our Colt road test.

At the time of writing, Mitsubishi announced the release of three more MIVEC engines.

Interestingly, the new Outlander (which is due for release in Japan in October 2005) will come powered by a 2.4-litre MIVEC engine that appears very similar to that already sold in Australia. However, with 125kW, the new engine is slightly more powerful than the current 4G69 2.4-litre MIVEC and is expected to achieve a 4-star LEV rating.

The Mitsubishi new-concept minicar i (due for Japanese release in early 2006) will be powered by a turbocharged 660cc three-cylinder MIVEC engine. Class regulations limit engine power to 47kW and torque figures are yet to be finalised. This little buzzer is expected to earn a 3-star LEV rating and return around 15 percent better fuel economy than the current 3G83 turbo three-pot.

Finally, the yet-to-be-released Lancer Evolution 9 will also incorporate MIVEC variable inlet valve timing. Together with few other mechanical changes, the mighty Evo has now cracked 400Nm of torque.